The present invention relates to kiln cars used to fire ceramic items in a furnace such as a tunnel kiln. Ceramic items are usually molded in the "green" state with sufficient structural integrity to withstand moderate handling and then fired to produce the finished ceramic item. For many applications the uniformity of the physical properties of the items fired is extremely important and in practice this means that each item should experience essentially the same thermal exposure in terms of time and temperature. Since many of the items to be fired are relatively small, it is not practical to fire each individually and kiln cars have been designed to carry batches of green items into the kiln for firing. These cars typically comprise a box into which the items are loaded and a support chassis on which the box is mounted and moved into and out of the kiln, perhaps on a fixed rail system.
The box portion of the car is typically made from ceramic plates or blocks supported in a suitable manner. The plates are usually made from a ceramic capable of withstanding the temperatures encountered in the kiln and the repeated thermal cycling involved in moving items into and out of the kiln. Where a supporting framework is used this can be in form of a frame in which the plates sit or the supports may be provided by a plurality of posts or pillars which support the plates at their corners such that up to four are supported on each post. The ceramic blocks that provide the sides and the bottom of the box are more usually made of a relatively cheap ceramic. However such ceramics may be subject to plastic deformation at the high temperatures in the kiln and eventually become so badly distorted that they have to be replaced. While such blocks are cheap relative to the framework materials, they are not inexpensive. In addition the kiln car must be taken out of service while it is being reconstructed and this necessarily involves commercial penalties. Therefore anything that prolongs the life of a kiln car while improving the uniformity of the products fired therein and the ease of handling of the items before and after firing, would be very significant from a technical as well as commercial viewpoint. The present invention meets both these objectives.
In one aspect, the present invention relates primarily to the design of the box structure in which the green items are carried which allows the box to have a prolonged useful life and facilitates loading and unloading operations.
Another aspect of the invention provides a means of loading and unloading kiln cars which ensures minimum handling damage, uniform thermal exposure to the items fired and an enhanced durability of the car.